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A radioimmunoassay for the quantitation of bovine platelet factor 4 (PF4) has been developed for use on bovine plasma. The assay utilizes classical radioimmunoassay techniques; 50λ of standard or plasma are mixed with 250λ 125I- bovine PF4 and 250λ goat anti-bovine PF4 for two hours at room temperature. Antibody-bound PF4 is separated from free PF4 by precipitation with ammonium sulfate. The resulting standard curve has a least detectable dose of 50 ng/ml, a 50% intercept around 400 ng/ml, a range of 01000 ng/ml and is unaffected by the presence of heparin in samples. Plasma samples are collected using a two-Vacu- tainer technique employing Thrombotect™ collection tubes (Abbott Laboratories) which have been developed to minimize any in vitro platelet release. The mean PF4 concentration of 7 healthy control calves was 55 ng/ml with a range of 0 to 180 ng/ml. PF4 levels were measured serially in calves which had undergone artificial heart implantation.  In one calf with a pre-operative PF4 level of 99 ng/ml, the PF4 level increased to 638 ng/ml during post-surgical complications 7 days after surgery and subsequently decreased to 230 ng/ml after coumarin therapy 27 days after surgery. A similarly implanted calf without post-surgical complications had a pre-operative PF4 level of 180 ng/ml and a 20 day post-surgical level of 245 ng/ml. These data suggest that PF4 levels are elevated in post-surgical hypercoaguable states and that measuring PF4 provides a useful tool for monitoring the post-surgical patency of artificial surfaces such as prosthetic valves, artificial hearts, left ventricular assists and thoracic surgery in general. This program is under further investigation to increase the understanding of platelet involvement in such systems, to determine how long PF4 elevations exist prior tc the.onset of clinical symptoms and to follow the success or failure of anticoagulant therapies.

A Radioimmunoassay For The Quantitation Of Bovine Platelet Factor 4 And Its Use In Monitoring Artificial Heart Implants